Generally, a heating device having a structure in which a heating target material is pressure-contacted with an arbitrary heating body with interposition of a film body therebetween and the heating target material is moved with the film body and heated at the same time has been used in various apparatuses. For example, various image formation apparatuses such as a printer using an electrophotographic method, a copy machine, and a fax machine employ a heating fixing device of a contact heating type which performs fixation of unfixed toner images transferred from an image carrier such as a photoconductive drum to a recording material side. In the heating fixing device, a film heating fixation method in which the recording material is heated via a fixing film having a small thermal capacity from the viewpoint of recent power saving, and the like has been widely employed. According to the film heating fixation method, when the fixing film having a small thermal capacity and high thermal conduction efficiency is interposed between the heating body such as a heater and the recording material serving as a heating target material, the rise time of the apparatus can be shortened, and power consumption can be reduced.
In a heating fixing device employing such a film fixation method, as shown in FIG. 2 and FIG. 3 according to an embodiment of the present invention, a heating body 118e is attached to a part of a sliding surface (lower surface in the drawing) of a heating support member 118d so as to be exposed, and a pressure roller 118b is pressure-contacted with a heating surface (lower surface in the drawing) of the heating body 118e from the lower side of the drawing via a fixing film 118a which is circularly movably disposed. When rotary drive of the pressure roller 118b is performed, the fixing film 118a and a recording material P serving as a heating target material are dependently moved, and, at the same time, a heating fixation action of unfixed toner T on the recording material P is performed.
An arbitrary lubricant agent such as grease is applied on the inner surface side of the fixing film 118a so that the above described movement of the fixing film 118a is smoothly performed in this process. When the lubricant agent such as grease is interposed between the fixing film 118a and the sliding surface of the heating support member 118d and the heating surface of the heating body 118e, the slidability between the members is improved.
However, such a lubricant agent comprising grease or the like has a tendency that, along with heating and temperature increase, the viscosity thereof is lowered and the fluidity thereof is increased, and an appropriate pressure is applied when the recording material P serving as a heating target material is caused to pass therethrough. Therefore, along with elapse of usage time, sometimes, the lubricant agent is moved from a center region in a longitudinal direction (image formation width direction) orthogonal to the movement direction of the fixing film 118a toward outside regions, and the lubricant agent leaks to outside from both ends in the longitudinal direction of the fixing film 118a. The lubricant agent leaked to outside in this manner may be a cause of deterioration in image quality, for example, the lubricant agent adheres to the outer surface of the fixing film 118a and deteriorates the detachability of the recording material P, or the lubricant agent adheres to the surface of the recording material P and the adhesion mark thereof is formed as an image.
Particularly, when the recording material P having a narrow size is caused to continuously pass through the center region of the longitudinal direction (image formation width direction) of the heating body, the temperature of the both-end regions, which are non-passage regions, is increased than the temperature of the center region, which is the passage region of the recording material P. The lubricant agent of the both-end regions (non-passage parts) of which fluidity is increased along with the temperature increase often leaks to outside from the both end portions of the longitudinal direction of the fixing film 118a. As a result, the amount of the lubricant agent in the both-end regions is reduced, and unevenness is caused in the distribution of the retention amount of the lubricant agent between the center region and the both-end regions. In the both-end regions in which the amount of the lubricant agent is reduced, the slidability between the fixing film 118a and the heating body 118e is deteriorated, thereby damaging the inner surface of the fixing film 118a and generating abnormal noise, and the reduction in the amount of the lubricant agent sometimes leads to shortened life of the equipment.
In order to solve such problems, for example in a heating device disclosed in Japanese Patent Application No. 1997-101695, a plurality of bosses or grooves are provided in an upstream side of a heating body, thereby preventing oozing of grease (lubricant agent) from both-end portions of a fixing film. However, in this device, the bosses or grooves are disposed in a region in which the heating temperature is comparatively low and fluidity of the lubricant agent is not good, in other words, in upstream side of the fixing film movement direction; therefore, the lubricant agent cannot be sufficiently spread in the longitudinal direction, a tendency that the lubricant agent is concentrated in a center region is generated, and friction of the fixing film with respect to the bosses or grooves is large.
Moreover, since the above described fixing film is pressure-contacted with a rotating pressure roller and rotated in a dependent manner, the fixing film has a tendency that it is strongly pulled toward the portion pressure-contacted with the pressure roller. Therefore, when the plurality of bosses or grooves are provided in the upstream side of the heating body like above described preceding literature, the inner surface of the fixing film strongly abuts edges of grooves on the surface of a heating support body; thus, there is a possibility that, for example, the inner surface of the fixing film is damaged, and the life of the fixing film is shortened.
Therefore, it is an object of the present invention to provide a heating device and an image formation apparatus capable of lengthening the life of equipment by facilitating spreading of a lubricant agent in the direction orthogonal to a film body movement direction of a fixing film or the like and eliminating lubricant agent leakage and capable of preventing generation of abnormal noise due to contamination or lubricant agent shortage due to lubricant agent leakage by a simple structure.